Rotary forges are used to hot work large shapes such as wrought billets, powdered metal products and some tubular shapes. The workpiece is initially heated in a gas fired or electrically heated box furnace and is then transferred by an appropriate conveyance system to the rotary forge. During forging, the manipulator rotates and advances the preheated workpiece into the rotary forge where the forging dies shape and refine the workpiece. The dies of the rotary forge operate quite rapidly, and in many instances the dies actually place more energy into the workpiece than is lost through adiabatic cooling. Thus, the forging operation can be carried out over relatively long periods of time until the desired product refinement is accomplished.
However, certain alloys require a relatively narrow hot working temperature range. Consequently, during forging, periodic reheating of all or a portion of the workpiece may be necessary, especially where the workpiece is of considerable length. Reheating may also be needed in selected areas, such as at the ends where the workpiece is grasped by the manipulator.
Certain types of products can only be forged in a single pass through the rotary forge. For example, in consolidating a powdered metal product, specialized tapered dies are used in the forge which permit only a single pass through the forge. Similarly, in forming a seamless tubular product over a mandrel, the forging is restricted to a single pass through the rotary forge in these instances. The length of the workpiece is limited, since the trailing end of the workpiece must not have cooled below the minimum working temperature by the time it reaches the forging dies.
Some prior art forging systems such as disclosed in U.S. Pat. Nos. 4,362,578 and 4,407,486 to Mills, et al., disclose off-line supplemental heating using induction heating coils. However, off-line heating is not feasible with a rotary forge having single pass dies. The trailing end of a single pass workpiece must be reheated in-line within the rotary forge since a portion of the workpiece has passed through the forge making transfer of the workpiece to an off-line supplementary heating system impossible.
It is therefore an object of the present invention to provide a rotary forging apparatus and method which can reheat and refine the grain structure of a workpiece inline with the path of travel of the workpiece through the forge.
It is a further object of this invention to provide a rotary forge where both forging and reheating of a workpiece can be accomplished simultaneously on different areas of the workpiece as it moves through the rotary forge.
It is another object of the present invention to provide a rotary forge having a suitable induction heating coil which selectively moves from an operative position surrounding the path of travel of the workpiece as it enters the rotary forge to an inoperative position away from the path of travel of the workpiece into the forge.